Barrier structure for food

ABSTRACT

A barrier laminate useful for the formation of orange juice and citrus beverage cartons is provided. The laminate provides a skin coat of a MDPE which provides a barrier to water vapor transmission through the laminate. The reduced water vapor flow decreases the bulge rate of the resulting carton.

[0001] may be mistakenly perceived by consumers as indicative of anexpired or spoiled product.

[0002] Heretofore, it was widely held that the bulge properties ofcartons were best controlled by increasing the thickness or stiffness ofthe underlying paperboard substrate. In accordance with the presentinvention, it has been found by applicants that by reducing the moisturetransmission rate, particularly moisture passing through the interiorsurface of a sealed carton, offers significant improvements in the bulgeproperties of the carton. Further, it is possible to provide a cartonhaving a highly effective oxygen barrier layer which, in combinationwith the water vapor barrier, provides a cost effective desirable cartonfor use with juice, citrus products, milk, and other high liquid contentfood products.

[0003] A variety of barrier structures and food packages are knownwithin the art.

[0004] For instance, U.S. Pat. No. 4,753,832 is directed to a barrierlaminate suitable for citrus beverages which has an innermost beveragecontacting surface comprising a thin layer of glycol-modifiedpolyethylene terephthalate (PET-G) which provides improved oxygenbarrier properties as opposed to an uncoated substrate.

[0005] U.S. Pat. No. 4,513,036, which is incorporated herein byreference, discloses a barrier laminate applied to a paperboardsubstrate comprising a web of propylene polymer adjacent to a foodcontact layer of an olefin polymer. An outer surface of the paperboardsubstrate is coated with a layer of a heat sealable olefin polymer. Thestructure sets forth a laminate having improved properties in retainingd-limonene along with improved retention of vitamin C levels.

[0006] U.S. Pat. No. 4,977,004, incorporated herein by reference,discloses a barrier liner for food packages comprising twin layers ofethylene-vinyl alcohol copolymers (EVOH). One layer is interposedbetween two moisture barriers such as high density polyethylene (HDPE),EVOH compatible adhesives, or low density polyethylene (LDPE). Theinnermost layer of EVOH provides a solvent barrier against loss offlavor components while the second EVOH layer serves as an oxygenbarrier.

[0007] While there are a variety of barrier laminates directed toimparting protective properties for preventing loss of flavoringcomponents, vitamin C, and barriers to reduce oxygen transmissionthrough the laminate, there remains room for variation and improvementwithin the art.

SUMMARY OF THE INVENTION

[0008] The present invention provides a barrier structure suitable forconverting into packages for foods and beverages which are economical,have good heat-sealing properties, exhibit low oxygen and water vaporpermeability, and provide protection against carton bulge or creep.

[0009] In its broadest embodiment, the barrier structure of the presentinvention comprises a food contact layer or “skin coat” of a mediumdensity polyethylene (MDPE) in which the MDPE is attached by an adhesivetie layer to a polyamide barrier layer. The polyamide barrier layer isattached directly along one surface to an inner paperboard surface. Thepolyamide layer and adjacent tie layer offer useful oxygen and watervapor barriers respectively. The MDPE skin coat provides an additionalwater vapor barrier and which further provides an essential oil barrierwhich reduces scalping, i.e., the absorption of d-limonene by theinterior board coating.

[0010] These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A full and enabling disclosure of the present invention,including the best mode thereof, to one of ordinary skill in the art, isset forth more particularly in the remainder of the specification,including reference to the accompanying drawings.

[0012]FIG. 1 is a perspective view of a juice carton in accordance withthe present invention.

[0013]FIG. 2 is a cross section taken along line 2-2 of FIG. 1 settingforth a laminate board structure of the present invention.

[0014]FIG. 3 is a graph depicting the increase in carton bulgeproperties over time of control stock cartons and trial cartonscontaining orange juice and fruit juice products.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] Reference now will be made in detail to the embodiments of theinvention, one or more examples of which are set forth below. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, can be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncover such modifications and variations as come within the scope of theappended claims and their equivalents. Other objects, features, andaspects of the present invention are disclosed in, or are obvious from,the following detailed description. It is to be understood by one ofordinary skill in the art that the present discussion is a descriptionof exemplary embodiments only and is not intended as limiting thebroader aspects of the present invention, which broader aspects areembodied in the exemplary constructions.

[0016] As used herein, the terms “inner” and “outer” are used todescribe and clarify relative positions of various layers of theresulting laminate. “Inner” refers to a position or layer along thecarton interior. The term “skin coat” refers to the innermost layer ofthe laminate/carton and provides the food contact surface. Similarly,“outer” is used to indicate a layer or surface closest to the gloss orexterior surface of the laminate/carton.

[0017] As used herein, MDPE refers to a polyethylene having an averagedensity level ranging from about 0.926 to about 0.940. The MDPE isprepared by mixing 55 percent by weight of an LDPE with 45 percent byweight of an HDPE. The resulting mixture is thereafter extruded as asingle layer of MDPE. The resulting MDPE has an overall greater densitythan the LDPE materials which have been conventionally used in theformulation of barrier layers. The higher density values of the MDPEimparts improved water vapor barrier properties while maintaining aninner surface which can be readily heat sealed using conventionalmethods and equipment.

[0018] It has been discovered that a barrier laminate suitable for foodand beverage barrier structures can be provided by a paperboardembodying the barrier structure as illustrated in FIGS. 1 and 2. As seenin FIG. 2, the paperboard used in the finished carton of FIG. 1comprises a fiber layer 10 which is sandwiched between an extruded MDPElayer 12, forming an exterior gloss surface, and an extruded innerpolyamide layer 14. As best seen in FIG. 2, the polyamide layer 14 isattached directly to the inner board surface 10. An adhesive tie layer16 joins the inner surface of nylon layer 16 the adjacent skin layer ofMDPE.

[0019] The preferred board structure can be provided by any conventional“juice board” or “milk board” which is a paper fiber board havingconventional sizing agents added to provide enhanced wet strength.Generally, board structure varies from about 150 to about 320 pounds per3,000 square feet though paperboard having greater or lesser weightscould be used for various applications. One having ordinary skill in theart will appreciate that the primary function of the paperboard is toprovide an overall structurally sound and rigid package.

[0020] As seen in FIGS. 1 and 2, the paperboard 10 is laminated betweenan outer extruded layer of MDPE 12 and an inner surface layer 14 ofpolyamide. The gloss, exterior surface of the MDPE layer 12 is appliedat about 16 pounds per 3,000 square feet of board and provides for aresulting package having good external moisture barrier properties, highgloss, and an abuse resistant impact surface. The inner polyamide(nylon) layer 14 is applied directly to the board 10 at a coating levelof about 3-5 pounds per 3,000 square feet and more preferably at about 5pounds per 3,000 square feet. Applying the nylon layer 14 directly tothe board 10 provides for good oxygen barrier properties.

[0021] Adjacent the inner nylon surface layer 14 is a tie layer 16,preferably provided by a modified polyethylene resin such as Bynel E388™ or Flexar 175 (Equistar), which is applied in a range of about 3 toabout 5 about 3 to about 5 pounds per 3,000 square feet of board. Thetie layer 16 is used to adhere the inner nylon surface layer to theadjacent MDPE skin coat layer 18. The MDPE skin layer 18 is applied at arate of about 20 pounds per 3,000 square feet of board. The MDPE skinlayer provides the inner laminate food contact surface. In accordancewith this invention the MDPE provides useful properties as a barrieragainst water vapor transmission. Further, the MDPE skin layer has alsobeen found to minimize the absorption/migration of an essential citrusflavoring oil, d-limonene, when compared to lower density polyethyleneskin layers. Further, the MDPE skin layer possesses good heat sealingproperties and provides a workable finish for the subsequent handlingand converting of the laminated board stock into erect, fillablecartons.

[0022] The structure seen in FIGS. 1 and 2 and as discussed above, iseasily applied to board stock through conventional extruding techniquesand equipment. The resulting structure has been found to offer a usefulbarrier structure for orange juice and related products in that thefilled and sealed cartons exhibit low oxygen transmission rates, hasgood resistance to water transmission, has increased resistance to creepof bulge of the carton, possesses good resistance to scalping ofd-limonene, and maintains effective levels of L-ascorbic acid (vitaminC).

Comparative Example 1

[0023] To illustrate the properties of the laminate and carton describedabove, comparative studies of a carton made according to the presentinvention (“trial examples”) were compared to a standard structure asconstructed according to the teachings of U.S. Pat. No. 4,835,025, whichis incorporated herein by reference. The standard carton has aconfiguration of:

[0024] 16# LDPE\280# board\5# nylon\5# tie\16# LDPE

[0025] The trial structure according to the present invention isconstructed of:

[0026] 16# MDPE\280# board\5# nylon\5# tie\20# MDPE

[0027] Standard ½ gallon containers were constructed from the standardand trial board stock set forth above. The containers were evaluated foroxygen transmission rates according to ASTM method D-3985 in whichpenetrating oxygen levels are determined for container samplescontaining a nitrogen gas.

[0028] The control board and the trial board were further evaluated forwater vapor transmission using TAPPI T-557 (PM-951) which corresponds toASTM Standard F1249-90. The test measures the partial pressureconcentration of water vapor which permeates through the barrier fromthe wet side to the dry side of the laminate. Measurements were madeusing MOCON Permatran equipment.

[0029] The oxygen transmission values of the trial board are equal to orbetter than the values of the commercially available control board. Thetrial board had an average oxygen transmission value of 4.85±0.1cc/m²/day compared to the values from the control board stock of 5.0±0.1cc/m²/day.

[0030] Consistent with the higher density of the MDPE, the trial boarddata indicated an approximate 7 percent reduction in the water vaportransmission rate compared to the control board. As discussed below, theimprovement in water transmission rate is believed to correlate with theimproved resistance to bulge properties of containers constructedaccording to the present invention.

[0031] Bulge Test Data

[0032] The control and trial barrier structures were also evaluated forbulge resistance. A series of individual one-half gallon cartons ofcontrol and trial barrier boards were separately filled with orangejuice and a fruit punch product and monitored over a twelve-week periodin a refrigerated cold room. Weekly measurements were made usingcalipers for each filled carton's length and width which, for therectangular cartons, are of substantially equal lengths. The average(mean) values for each sample carton over the twelve week time periodare illustrated graphically in FIG. 3. The orange juice control (A) andfruit punch control carton (B) have a bulge increase of 0.269 and 0.206inches respectively over the twelve-week evaluation interval. The trialcontainers had a bulge increase of 0.119 inches and 0.133 inches for therespective orange juice and fruit punch containers. As best illustratedin the graph set forth as FIG. 3, the trial cartons demonstrated lessbulge than the control cartons.

[0033] The MDPE barrier layer provides an excellent water vapor barrierwhen compared to lower density polyethylene (LDPE) which is frequentlyused as a barrier material within conventional juice and beveragecartons. While conventional teachings suggest that bulge improvementsare obtained by increasing the stiffness of the underlying board, thepresent invention establishes that significant improvements in cartonbulge can be obtained by the establishment of an improved moistureresistant barrier between the board and the interior wet surface of thecontainer. Thus, by decreasing the passage of water vapor through thelaminate structure, improvement in the bulge resistance properties ofthe carton can be obtained.

[0034] As seen in reference to the FIG. 3 graph, the improvement inbulge resistance in the trial board becomes more pronounced over time.While not wishing to be limited by theory, it is believed that evenmodest improvements in water vapor transmission rates may increase thebulge resistance of the resulting carton. The tendency of cartons tobulge appears to be a cumulative phenomenon which correlates with thevolume of water vapor transmission over time. Accordingly, the modestreduction in water vapor transmission rate through the paperboardresults in improved bulge resistance of the carton, the improvementbecoming more pronounced as time elapses.

[0035] The present invention recognizes that the average density of thepolyethylene barrier layer can be increased over the LDPE ranges usedwithin the prior art. The increased density achieves a barrier layerhaving improved resistance to water vapor transmission. Further, theMDPE maintains the useful ability to be heat sealed during commercialpackaging operations.

[0036] While not separately set forth, evaluations of the trialstructures for retention of vitamin C levels and d-limonene levels fallwithin the typical and useful commercial ranges associated withconventional paperboard containers for orange juice and beverageproducts. Further, the improved barrier properties and the resultingcarton can be used in conjunction with additional layers and laminatesto provide additional variation in useful laminates.

[0037] Although preferred embodiments of the invention have beendescribed using specific terms, devices, and methods, such descriptionis for illustrative purposes only. The words used are words ofdescription rather than of limitation. It is to be understood thatchanges and variations may be made by those of ordinary skill in the artwithout departing from the spirit or the scope of the present invention,which is set forth in the following claims. In addition, it should beunderstood that aspects of the various embodiments may be interchanged,both in whole or in part. Therefore, the spirit and scope of theappended claims should not be limited to the description of thepreferred versions contained therein.

That which is claimed is:
 1. A barrier laminate comprising: a paperboardsubstrate having a first surface and a second surface, the secondsurface being opposite the first surface; a nylon barrier layer applieddirectly on the first surface of paperboard substrate; a tie layerapplied to an inner surface of the nylon barrier layer; a medium densitypolyethylene barrier layer applied directly onto an inner surface of thetie layer, the medium density polyethylene barrier layer furtherproviding a heat seal layer.
 2. The barrier laminate according to claim1 wherein the medium density polyethylene has an average density ofbetween about 0.926 and about 0.940.
 3. The barrier laminate accordingto claim 2 wherein the MDPE is applied to the paperboard substrate atcoating weight of between about 3-5 pounds per 3000 square feet.
 4. Thebarrier laminate according to claim 1 further comprising a second layerof MDPE applied to the second surface of the paperboard substrate.
 5. Afoldable laminated blank comprising: a substrate material selected fromthe group consisting of paper, paperboard, fiberboard, and bleachedkraft paper having a first side and a second side opposite the firstside; a nylon barrier layer attached along an outer surface directly tothe first side of the substrate material; a product contacting surfaceopposite an inner surface of the nylon barrier layer, and comprisedsubstantially entirely of a layer of MDPE, the layer of MDPE providing aheat sealable barrier.
 6. The barrier laminate according to claim 5further comprising a tie layer connecting the inner nylon barrier layersurface to an outer surface of the MDPE product contacting layer.
 7. Thebarrier laminate according to claim 5 wherein the medium densitypolyethylene barrier layer has an average density of between about 0.926and about 0.94.
 8. The barrier laminate according to claim 6 wherein theMDPE is applied at a coating weight of between about 3-5 pounds per 3000square feet.
 9. The barrier laminate according to claim 5 furthercomprising a second layer of MDPE applied to the second surface of thesubstrate.